Top BIOS (Basic Input/Output System) Interview Questions and Answers

Understanding BIOS is crucial for anyone looking to build a career in IT. As the firmware interface between a computer’s hardware and software, BIOS plays a vital role in the boot process and system management. In this article, we’ll explore some of the most common BIOS interview questions asked during technical interviews.

Whether you’re prepping for your first IT job or a seasoned pro looking to brush up, this list of 45 questions and detailed answers will help you master this topic Read on to learn what hiring managers want candidates to know about BIOS

What Does BIOS Stand For and What is Its Role?

BIOS stands for Basic Input/Output System. It is firmware stored on a small memory chip on the motherboard and is the first software to run when the computer powers on.

The main roles of BIOS are

• Performing a power-on self-test (POST) to ensure hardware components like CPU, RAM, hard drive are working properly.

• Initializing and establishing communication between hardware like video card, keyboard, mouse.

• Loading bootloader software from storage into memory which then starts the operating system.

• Providing runtime services like power management and accessing storage via legacy BIOS interrupts.

In essence, BIOS serves as an intermediary between the hardware components and operating system software of a computer system.

What Happens During the POST Process?

When a computer first turns on, the BIOS runs a series of diagnostic tests called the POST or power-on self-test. This checks for basic functionality of core hardware components like the CPU, RAM, motherboard, keyboard, hard drive etc.

Specifically, POST checks that:

• The CPU is plugged in and operational.
• Memory chips are detected and readable/writable.
• Integrated peripherals like keyboard, mouse, and graphics card are working.
• Storage devices are correctly connected and can be accessed.

If everything checks out, it hands control over to the bootloader to load the OS. If not, it displays error beep codes or on-screen messages to indicate faulty hardware.

How Can You Access the BIOS Settings?

To access BIOS settings, you need to press a designated key like F2, Delete, or F12 during the boot process. This key varies by motherboard or laptop manufacturer. Pressing it takes you to the BIOS setup screen before Windows launches.

Here you can configure boot order, enable or disable hardware components, set CPU clock speeds, voltages, RAM timings, power management options and more. After making changes, save and exit BIOS to have them take effect on next boot.

What is CMOS and What Role Does it Play With BIOS?

CMOS stands for Complementary Metal-Oxide Semiconductor. It is the memory chip on motherboards that stores BIOS settings and configuration information like date, time, hardware settings, and boot device order.

This data needs to be retained even when the system is powered off. So the CMOS chip has a small onboard battery to provide continuous power.

On every reboot, BIOS loads the hardware configuration data from CMOS. This way BIOS knows the correct user-defined settings to initialize during the boot process.

How Can You Update the BIOS?

There are a few methods to update BIOS:

Within Operating System: Download the latest BIOS file from manufacturer website to USB drive. Reboot to BIOS, locate utility to flash from USB.

Bootable USB: Download the BIOS file on another PC. Create bootable USB drive, copy file to it. Boot target PC from USB, then flash BIOS.

BIOS Flashback: Some motherboards support flashing by just having the BIOS file on a USB, inserting into the designated port and pressing the flashback button.

No matter the method, it’s crucial to avoid interruptions during the flashing process and use a stable power source. An incomplete update can corrupt the BIOS and prevent booting.

What Happens if Incorrect Settings are Applied in BIOS?

Changing the wrong BIOS parameters can lead to:

• Boot issues: Incorrect boot order or disabling storage controller could cause failure to load OS.

• System instability: Overclocking CPU/RAM incorrectly could result in crashes, freezes or data corruption.

• Hardware damage: Too high voltages can damage CPU or RAM permanently.

• Access problems: Disabling ports or misconfiguring devices could cause peripherals to not work.

• Security risks: Weak passwords or enabling external booting could allow malicious access.

Fortunately, resetting BIOS to default values usually resolves such issues. Flashing the BIOS may help if settings caused corruption.

How Does BIOS Identify System Hardware?

BIOS identifies hardware via a process called auto-detection. This occurs during POST.

The auto-detection logic is pre-programmed into the BIOS firmware. It probes certain addresses, ports and buses to check for connected devices. For example, it checks for keyboard at specific ports or looks for PCI devices.

Any compatible device found is then assigned system resources like IRQs, I/O ports, DMA channels and memory addresses. This process allows the OS to later interact with devices standardized resources, regardless of the specific hardware.

What Role Does BIOS Play in Booting Different Operating Systems?

The boot process for different OSs contains these common steps handled by BIOS:

1. POST validates hardware is functional.

2. Master Boot Record(MBR) is read from storage into memory.

3. Bootloader located in MBR uses instruction specific to the OS to start loading it.

4. BIOS runtime services support booting by providing access to hardware via legacy interrupts.

5. Once kernel is loaded, BIOS hands-off control to the OS.

So while the boot instructions differ between operating systems, BIOS plays an essential, standardized role in the early booting stages for all OSs before handing over control.

What Are Some Typical Settings Configurable via BIOS?

Some typical settings that can be changed in BIOS are:

• Boot order: Priority sequence of bootable devices like hard disk, USB, CD-ROM.

• Secure Boot: Enables checking legitimacy of boot software via digital signatures.

• Overclocking: Increasing CPU clock speed, voltage and RAM speed beyond factory specs.

• SATA mode: Toggles between AHCI and IDE compatibility modes for storage devices.

• Power management: Suspend, hibernation and wake settings to conserve energy.

• Integrated Peripherals: Enable or disable onboard devices like Wi-Fi, Bluetooth, RAID card.

• Legacy USB support: Enable booting from legacy USB devices in addition to UEFI.

What Are Some Differences Between Legacy BIOS and UEFI?

Some key differences between legacy BIOS and UEFI:

• Storage support: UEFI can boot from drives larger than 2.2TB which legacy BIOS cannot.

• Speed: UEFI boots faster due to its more modern architecture and graphics interface.

• Security: UEFI has added security like Secure Boot and integrated antivirus.

• Functionality: UEFI provides more diagnostic info, remote troubleshooting, backups and optimizations.

• Graphical interface: UEFI provides mouse support, photos and animations for an improved experience over text-based BIOS.

• Modularity: UEFI drivers and features can be updated independently without replacing the whole firmware.

What Happens During a BIOS Update?

When updating BIOS, the following key steps occur:

1. The flash utility overwrites the existing BIOS chip contents with the new firmware code.

2. Settings like boot order, overclocked values are reset to default to avoid conflicts.

3. Updated ACPI modules, hardware initialization routines and drivers are installed.

4. The checksum stored in CMOS used to validate BIOS integrity is recalculated.

5. Once flashing completes, BIOS reset itself. System does a cold boot to load new BIOS version from start.

6. During POST, new values and defaults like system time will be loaded from CMOS.

What Are Some Troubleshooting Tips for a Computer That Won’t Boot?

Some troubleshooting tips for a computer that won’t boot:

• Check if power light/fans turn on – if not, an issue with power or motherboard.

• Listen for beep codes during POST. Look these up to pinpoint faulty hardware.

• Try booting from a bootable USB or CD. If it works, could indicate hard drive failure.

• Reset BIOS to default settings to resolve any conflicts between old config and new hardware.

• Reseat RAM, GPU and cables to fix any loose connections.

• Remove all non-essential hardware and attempt to boot with only basics like CPU, one RAM stick, integrated graphics.

• If above steps fail, test hardware individually on another system to identify faulty component.

• Replace CMOS battery and reset BIOS again if settings